// ProblemSetSystem.java
public class Main {
    public static void main(String[] args) {
        ProblemSet problemSet = new ProblemSet();
        for (int i = 0; i < 50; i++) {
            problemSet.addProblem(ProblemFactory.createAdditionProblem());
            problemSet.addProblem(ProblemFactory.createSubtractionProblem());
        }
        problemSet.displayProblems();
    }
}